Commercially Important

AUSTIN S. BRUNJES' AND CLIFFORD C. FURNAS. Yale University, New Haven, Conn. N A PREVIOUS article of this series (I) data were presented for the ...
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Commercially Important Systems of Organic Solvents Vapor-Liquid Equilibrium

..

geneous and the heterogeneous phases was determined by two different methods : METHOD1. -4series of known mixtures of butanol and butyl acetate was made up in weighed, glass-stoppered, Erlenmeyer flasks. A small buret provided with a stopper fitting snugly into the necks of these flasks was filled with distilled water and connected to one of them. The water was slowly added dropwise at a temperature slightly below 25OC. until cloudiness first appeared. While the water was being added, the flasks were shaken vigorously. When the cloudiness appeared, one more drop of water was added, and the flasks were immersed in the thermostat and allowed to come to temperature. The mixtures were thus just saturated at 25OC. The criterion for saturation was a small drop of water in excess. Mixtures which had an excess of more than the small drop were discarded. The flasks were weighed again; the increase in weight was the water picked up by the mixtures. METHOD2. An apparatus was developed which proved quite satisfactory and more rapid than shaking flasks by hand (Fi ure I). It consisted of a small Pyrex glass bulb 2 inches (5 cmfi in diameter provided with a small stopcock at the bottom and two necks at the top. One neck had a ground joint to fit a small buret; the other somewhat larger neck was provided with a mercury seal and a glass stirrer. The stirrer was run by a small variable-speed motor. The apparatus containing a weighed mixture of alcohol and acetate was placed in the thermostat, the buret attached, and the stirrer started. Water was added dropwise until the cloudiness just appeared. The speed of the stirrer was increased for several minutes to break up the cloudiness. The stirrer and buret were then removed and the opening in the necks closed with glass stoppers provided for the purpose. The apparatus was removed from the thermostat, dried, and weighed t o determine the amount of water added. A small loop blown in the top of the bulb served to suspend the

Data for the Ternary System n-Butanol-

n-Butyl Acetate-Water AUSTIN S. BRUNJES' AND CLIFFORD C. FURNAS Yale University, New Haven, Conn.

N A PREVIOUS article of this series ( I ) data were presented for the vapor-liquid equilibrium relations of the system n-butano1-n-butyl acetate. I n the present paper the equilibrium relations are given for the ternary system including water as the third component. Rosanoff, Schulze, and Dunphy (9) studied ternary systems and presented their results by plotting the two binaries and several ternary mixtures for each different boiling point on isosceles right-angle triangles, gjving the compositions of the liquid and the vapor in equilibrium with it. I n this paper an attempt is made to correlate the data obtained in a new and different way in the hope that i t may be useful in designing fractionating equipment.

The specific gravities and compositions for all possible mixtures of n-butanoln-butyl acetate-water were determined at 25/25' C., and plotted on rectangular and triangular coordinates. The method of Stockhardt and Hull was used to determine vapor-liquid equilibrium curves for saturated and unsaturated mixtures of n-butanol-n-butyl acetate-water. The results were correlated by two new methods. Data for the composition of saturated mixtures of n-butanol-n-butyl acetate with water at the boiling point were also determined and presented, and the composition of the heterogeneous azeotrope of n-butyl acetate and water was established. This mixture boils at 90.5"C. (760 m m . pressure), and has a composition of 29.44 mole per cent acetate and 70.56 mole per cent water. The ternary system possesses no true azeotropic mixture.

Determination of Water-Saturation Curve at

20" c.

The introduction of water as third component to the system n-butanol-n-butyl acetate-water produces a heterogeneous system over a considerable range; hence it was necessary to study the solubility relations of the system before distillation data could be interpreted. The butyl acetate is practically insoluble in the water, and likewise the water is nearly insoluble in the acetate. For the alcohol-water pair, Hill and Malisoff (5) determined the mutual solubilities of water and alcohol by volumetric measurements a t 25' C. and found that the water layer contained 7.37 per cent alcohol b y weight, and the alcohol layer contained 20.27 per cent water b y weight. Stockhardt and Hull (10) determined the solubility of water in the alcohol layer at 25OC. by gravimetric methods and found it to be 20.5 per cent water and 79.5 per cent alcohol. I n the present investigation i t was necessary to know the water saturation values not only for pure butanol and butyl acetate, but for mixtures of all portions of these two components. The saturation line or boundary between the homo-

' Present address, The Lummua Company, New York. 57:

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INDUSTRIAL AND ENGINEERING CHEMISTRY

n

apparatus by a fine platinum wire from the balance arm

during weighing. A similar bulb containing shot was used as a counterpoise.

In a similar manner pure distilled water was saturated with butanol and then with butyl acetate. The solubility was so small in b o t h cases t h a t it w a s deemed unnecessary to determine more than the two points to fix the position of the upper limits of the heterogeneous phase. The specific gravity of each of the saturated mixtures was determined immediately after the weight of the added water had been found. The results of these d e t e r m i n a t i o n s are presented in Table I, on both the weight per cent and the mole per cent bases. The data were plotted in three different ways in order to smooth out all points and obtain the best line for plotting on a largescale working chart. The three plots were: (1) the FIGURE 1. APPARATUS FOR DETERMININGAMOENT OF p e r c e n t a g e of water to WATER REQUIREDTO SATUsaturate mixtures of alcohol RATE MIXTERES OF BUTANOL and acetate us. the percentAND BUTYL ACETATE age of alcohol (weight per A . Bearing surface cent), ( 2 ) t h e specific B. Glass bearing C . Mercury seal gravity vs. the weight per D . Detachable buret E . Standard tapers to fit ground cent of alcohol in the satustoppers rated mixtures, and (3) the F. Diameter, 5 cm. specific g r a v i t y vs. t h e weight - -per cent of mater in the saturated mixtures. In plotting the h a 1 chart for use, each point chosen had to check the other three charts to satisfy the correct line. Thus, there was a triple check on the accuracy of the data. All doubtful points were thrown out and the compositions rerun. The data for specific gravity 03. per cent butanol are presented as the saturation line in Figure 2. The compositions a t saturation are shown on the triangular chart (Figure 3).

/o

20

I*)

4

$0

Percent Bufanol

60

& We/ghf

70

80

9o/w

FIQURE2. SPECIFIC GRAVITY us. PER CENT BY WEIGHTOF BUTANOLFOR DIFFERENT WATER CONTENTSIN THE SINGLE-PHASE SYSTEM BUTANOL-BUTYL ACETATE-WATER

VOL. 28. NO. 5

TABLEI. COMPOSITION AND SPECIFIC GRAVITYOF WATERSATERATED MIXTURESOF BUTANOL,BUTYLACETATE,AND WATERAT 25' C. Run

58 1 72 73 59 70 2 13 3 14 4 25 15 5 16 6 17 24 1s 8

19 22 20 10 12 21 11

-Weight Per CentBuOH BuOAc Hz0

0.00 0.00 0.00

99.43 0.56 99.71 0.28 0.83 99.17 0.00 0.94 99.06 4.56 93.66 1.77 7.32 0.00 92.67 9.24 90.12 0.63 13.37 85.32 1.31 18.29 79.35 2.34 22.36 73.92 33.71 27.20 68.50 4.30 28.82 65.61 5.55 30.41 64.24 6.33 35.45 58.06 6.47 39.20 52.80 8.00 43.20 47.80 9.00 47.66 42.30 10.13 51.46 37.52 11.00 55.26 32.86 11.86 59.41 27.84 12.74 64.24 22.39 13.35 66.90 18.76 14.35 13.80 15.21 70.98 74.23 9.10 16.66 8.80 17.17 74.01 4.40 18.30 77.30 80.25 0.00 19.75

-Mole BuOH

Per CentBuOAc H20

Sp. Cr.,

0.00 0.00 0.00 0.00 6.37 1.89 13.33 11.85 23.30 27.72 30.71 30.83 32.60 35.75 37.07 39.03

96.41 98.22 0.13 0.15 83.45 0.00 82.92 80.21 64.44 58.46 49.31 44.74 43.90 37.35 31.82 27.53 23.48 19.82 16.76 13.69 10.69 8.66 6.14 3.96 2.99 1.80 0.00

0.87871 0.87754 0.9987s 0.9991r

49.89 50.74 49.32 49.76 49.70

3.59 1.78 99.87 99.86 10.1s 98.11 3.75 7.94 12.26 13.83 19.98 24.43 23.60 26.87 31.11 33.44 35.00 37.51 39.02 40.45 41.15 42.81 43.97 45.30 47.69 48.44 50.30

25/25

0.86390 0.86371 0.86371 0.86132 0.8593s 0.85727 0.85604 0.85508 0.85367 0,85244 0.85060 0.8498~ 0.8478s 0.8469s 0.84771 0.84700 0.84667

GRAVITY FOR UNTABLE11. WEIGHTPER CENTAND SPECIFIC SATURATED MIXTURESOF BUTANOL,BUTYLACETATE,AND WATER Run 26 68 27 62 63 64 69 65 66 67 29 30 38 31 32 33 46 34 35 52 53 54 55 57 37 39 40 41 42 43 44 45 40 47 48 49 50 51

---Weight BuOH 81.66 82.05 76.83 85.48 78.33 69.44 72.84 85.62 * 78.38 71.01 87.85 82.53 78.37 77.32 73.56 66.80 65.77 61.48 56.84 90.70 80.38 69.69 59.56 49.52 94.00 72.62 60.45 52.45 43.23 32.60 96.91 86.11 65.15 59.07 45.14 35.25 25.67 16.23

Per Cent-BuOAc

00.00 00.00

5.31 00.00 7.16 16.44 10.57 00.00 7.14 14.25 00.00 5.29 10.13 10.53 14.21 21.01 20.34 26.01 31.23 00.00 10.67 21.11 31.43 41.04 00.00 21.27 33.75 41.64 50.57 61.19 00.00 10.71 31.84 38.16 51.76 61.70 71.34 80.92

KzO 18.33 17.95 17.84 14.51 14.60 14.11 16.54 14.37 14.47 14.73 12.14 12.17 11.48 12,14 12.22 12.17 13.88 12.50 11.91 9.29 9.04 9.18 9.00 9.43 8.99 6.10 5.79 5.90 6.19 6.19 3.08 3.16

2.99 2.76 3.08 3.04 2.97 2.83

Sp. Gr., 25/26 0,84290 0.8422s 0.8458s 0.83591 0.8406a 0.84614 0.84680 0.83564 0.8405r 0.8458s 0.83187 0.83521 0.8368s 0.83864 0.8412r 0,84756 0.8356s 0.84976 0.85210 0.8286s 0.8328, 0.8399s 0,84640 0,8540s 0.82031 0.83396 0.83756 0.88726 0.85411 0.86167 0.81486 0.8214s 0.8344s 0.83810 0,84822 0.85491 0.86181 0.8686s

Next a series of mixtures containing a known amount of water, less than that required for saturation, were made up and their specific gravities determined a t 25" C. These data are shown in Table 11. The data of Table I and I1 together with the specific gravity vs. weight per cent of alcohol on the dry basis are plotted in Figure 2 . From this plot the lines of constant specific gravity were scaled off, and the points for plotting included in Table 111. These data and the saturation lines are plotted on the isometric chart (Figure 3). Near the water apex of the isometric chart the other boundary of the heterogeneous phase may be seen. The data for this line are plotted on a larger scale in Figure 4. The

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5 75

speciilc gravity data for this saturation Water Wufcr line are plotted in Figure 5. To use Figure 3 to determine the composition of any mixture of the three components, the specific gravity of the mixture is determined a t 25" C.; then the sample is saturated with water by either of the methods described, and the gravity Hctcrogcncous Reglm FIQURE 4. SATURATION is again determined. A straight edge is BTJTANOLLINEFOR SYSTEM laid from the water apex of the isometric AT BUTYLACETATE-WATER chart to the point on the saturation line 25" c. corresponding to the specific gravity a t saturation. If this line is extended until it cuts the constant specific gravity corresponding to that of the original sample, the point of intersection gives the composition of the original sample. The proof of this method lies in the well-known theorem BUTYLACETATE-WATER of geometry that, if a line is drawn from Weigh? Percent n-Bufum the apex of a n equilateral triangle to the To do this, mixtures of alcohol FIGURE5. SPECIFIC GRAVITY opposite base, it will divide the triangle so that the segments it cuts on any lines drawn parallel to that base will always and acetate were made up in OF WATERSATURATED WITH be in the same proportion. The diagrams and the method t h e s a m e w a y a s f o r the BUTARioL AND ACETATE were checked with known mixtures of the three components, binary system ( I ) , and SUBand the compositions checked within the accuracy of reading cient water was added to have two phases present a t the boilthe charts. ing point. A series of nine runs was made with the Othmer apparatus, Distillation Methods and Results and, when the results were computed, it was found that the Othmer (6,7) made no claim that his apparatus and method water content of the residue was always greater than the water content of the distillate. This behavior was contrary to qua& would work on a two-phase system; but it was thought that if sufficient agitation were maintained in the still pot by tative calculations made on the assumption that the system rapid ebullition and if the rate of distillat'on were fast enough was that of a simple steam distillation, with the boiling point of the alcohol-acetate phase higher than that of the water to prevent the two layers from separating in the receiver, phase. satisfactory results might be obtained. The first set of data determined was a liquid-vapor equilibrium curve for a series The data obtained on the two-phase saturated systems of saturated systems in which two phases were present in seemed unsatisfactory, but it was thought that the apparatus both the distillate and the residue a t the boiling temperature. might give satisfactory operation on a single-phase system with three components. Hence the water layer was removed from residue in the still body of the Othmer TABLE111. CONSTANT GRAVITY LINESFOR SYSTEM BUTANOLapparatus, and the single phase BUTYLACETATE-WATER was distilled. As t h e d i s t i l l a t e Weight Per Cent Weight Per Cent came over into the receiver and Sp. Gr.,25/25 BuOH BuOAc BuOH BuOAo Sp. Gr.,25/25 HzO HnO separated into two layers, the water 0,8100 97.20 2.80 0.00 42.20 57.80 0.00 0.8450 99.10 0.00 0.90'" 49.15 47.85 3.00 layer w a s c o n t i n u a l l y removed 55.30 38.70 6.00 61.75 29.25 9.00 until the distillate was a1so.a single 0.8150 88.90 11.10 0.00 96.15 0.85 3.00 67.70 20.30 l2.O0 layer; then t h e a p p a r a t u s w a s 95.55 3.45" 0.00 74.00 11.00 15.00 SO.00 2.00 18.00 allowed to come to equilibrium and 0 8200 80.50 19.50 0.00 0.00 19.00'" 81.00 samples were taken for analysis. 88.00 9.00 3.00 93.80 0.00 6.20Q 0.8500 35.00 65.00 0.00 The water content of the residues 42.10 54.90 3.0C 0.8250 72.50 27.50 0.00 48.15 45.85 6.00 of these runs was so low that the 17.30 79.70 3.00 54.45 36.55 9.00 60.00 28.00 12.00 compositions could not be accu7.50 86.50 6.00 91.35 8.65a 0.00 66.25 19.55 14.20a rately determined without resorting 0.8550 28.00 72.00 0.00 to saponification of the samples to 35.20 61.80 3.00 41.35 52.65 6.00 determine the ester content as a 0,8300 64.60 35.40 0.00 47.25 43.75 check on the gravity analysis. 71.50 25.50 3.00 51.00 28.25 78.45 15.55 6.00 The water content of systems that 85.00 9.00 6.00 21.25 79.75 0.8600 0.00 28.10 68.90 3.00 had only a single phase in residue 88.70 0.00 11 30a 34.50 59.50 67,60a .00 and d i s t i l l a t e was so low in all 0.8350 57.00 43.00 0.00 37.20 55.20 63.50 33.50 3.00 cases that the determinations were 70.75 23.25 6.00 0.8650 14.65 85.35 0.00 77.00 14.00 9.00 21.35 75.65 3.00 inaccurate. The Othmer method 82.75 5.25 12.00 24.50 71.25 4.25 was therefore abandoned, and that 86.15 13.85O 0.00 0.8700 8.20 91.80 0.00 of Stockhardt and Hull (10) given 50.50 0.00 13.30 84.90 1.80 a trial. On the several experiments 40.80 3.00 31.25 6.00 carried out with known mixtures, 21.75 9.00 0.8750 2.00 98.00 o,oo 12.80 12.00 4.25 95.00 0. gravity and saponification analyses 4.00 15.00 were made on the equilibrium mix16.45a 0.00 5 Saturated. tures and found to a g r e e v e r y I closely; hence t h e m e t h o d w a s

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INDUSTRIAL AND ENGINEERING CHEMISTRY

576

adopted in preference to that of Rosanoff, B a c o n , and White (8) b e c a u s e of i t s simplicity a n d greater rapidity. The a p p a r a t u s (Figure 6) consisted of a one-liter Pyrex distilling flask from which the side arm was removed; a short condenser was sealed in its place. This alteration was an improvement over the original apparatus of Stockhardt and FIGURE 6. APPARATUS FOR Hull because there was no DETERMINING DISTILLATION rubber connection exposed to EQUILIBRIA IN SYSTEMSCONthe action of the hot solvent TAINING Two LIQUIDPHASES vapors, and the compact unit could be s w u n g on a c l a m p from the distillation position t o the reflux position very quickly. The neck and sides of the flask were wrapped with a double layer of heavy asbestos rope cemented in place with water glass. Over this was a thin layer of asbestos cement such as is used on furnace piping. The apparatus was heated on a large electrical heater arranged with a short sheet-iron chimney so that the hot air rising from the heater passed up around the sides of the flask, keeping it nearly at the same temperature as the inside. Little or no condensation was ever noticed in the upper portion of the neck of the flask where it was most likely t o occur. Boiling tubes had to be placed in the flask when mixtures of two liquid phases were distilled in order to prevent local superheating and subsequent violent bumping of the liquid which would carry over into the condenser and thus destroy the accuracy of the results. This method of obtaining vapor-liquid equilibrium data depends upon distilling out a relatively small sample from a large amount of liquid and determining the composition of both the distillate and the residue. A known mixture of alcohol, acetate, and water was made up by weighing the separate components into a large tared Erlenmeyer flask. A 700 to 800-gram sample was taken each time. The volume of this sample was nearly a liter and would allow the distillation of four to five small fractions without seriously affecting the composition of the residue. The specific gravity of the sample was taken and recorded as a check on the weights and the chart. The sample was then placed in the apparatus with the condenser in the reflux position.

VOL. 28, NO. 5

The sample was gently boiled and allowed to reflux for half an hour; then the apparatus was placed in the distilling position, and forward distillation was started. The distillates were collected in 50-ml., tared, glass-stoppered funnels of the separatory type with the long bottom tube cut off directly under the stopcock. No more than five fractions were ever distilled out of a batch. The funnels were weighed and then placed in the thermostat until the two layers had separated at 25" C. The water layer was then removed, and the funnel was dried carefully and reweighed. The specific gravities of both the upper and lower layers of the distillate were next determined and their compositions ascertained from the charts (Figures 3 and 5). From these measurements the weights of the three components in each layer and then in the total distillate could be calculated. These weights subtracted from the original weights of each component

9

.Z .3 .4 .J .6 .7 .B .9 LO Mol Fraction n-Bufuno/ in fhe liquid, Dry 8m/5

0 .i

FIGURE 7 . VAPOR-LIQUIDEQUILIBRIA FOR SYSTEM BUTANOL-WATER-BUTYL ACETATE FOR VARIOUS CONSTANT PERCENTAGES OF WATER

present gave the amounts in the residue. The average weight and mole percentages for the run for both distillate and residue were then calculated for each component on both the wet and dry bases. The residue remaining in the distilling flask after the several samples had been distilled out was weighed, and its specific FOR RUN 31 TABLEIV. DATAAND CALCULATIONS g r a v i t y determined. A portion was then saturated with (Corrected barometric pressure, 761.8 mm.: average vapor temperature, 90.6' C.) I. Initial Sample water a t 25 C. and the gravity Weight, Grams Weieht again determined. The charts - Per Cent 320 0 . 39.97 (Figures 2 and 3) were used to BuOH 320.0 39.97 BuOAc find out if t h e c o m p o s i t i o n 160.5 20.05 Hz0 calculated from the last residue 800.5 Total sample 11. Distillate of the distillation checked with Weight per cent (upper layer): Weight per cent (lower layer) : that a c t u a l l y there. As a Weight, grams: BuOH 33.00 BuOH 3.8 81.6535 Funnel + sample further check on the accuracy, BuOAc 60.55 BuOAc 0.4 30.1300 Funnel empty HzO 6.45 another portion of the residue H 2 0 95.8 51.5235 Sample Weight, grams (upper layer): Weight grams (lower layer) : was saponified for ester conFunnel + upper layer 76.5222 BuOH 12.3394 BuOk 0.5369 37.3922 Upper layer tent. By this procedure any BuOAc 22.6409 BuOAc 0.565 14,1313 Lower layer batch of samples had a triple 2.4117 HzO 13,5378 Hz0 Pvanometer + lower 12.8763 Total BuOH Pycnometer + upper check to determine its composi5.7470 layer Total BuOAc 22.6974 layer 53.1076 3.7660 Pycnometer empty tion. Total Hz0 15.9495 Pycnometer empty 31.5828 1,9810 O

Sample Sp. gr., 25/25

0.99348

Sample Sp. gr., 25/25

Weight er cent (total distillate): BuOg BuOAc Hz0 Mole per cent (total distillate): BuOH BuOAc Hz0 111. Weight, grams (by difference): BuOH 307.1237 BuOAc 297.3026 Hz0 144.5505 Total residue 748.9768 Weight er cent: 41.00 BUOEF 39.69 BuOAc Hi0 19.30

21.5248 0.86176

Total sample

Wet Basis

Dry Basis

24.99 44.05 30.96

36.20 63.80

13.86 15.57 70.60 Residue

42.00 58.0

.4v. weight per cent: BuOH BuOAc Hz0

Mole per cent: BuOH BuOAc HzO

.

.

51.5232

I

Wet Basis

Dry Basis

40.49 39.83 19.68

50.41 49.59

27.58 17.29 55.12

61.40 38.60

...

...

While making a material balance after each series of distillations, a discrepancy of about a gram in the 800gram sample taken was found to be the usual difference. This loss was attributed to the fact that, when starting up a refluxing period, the air in the flask which was displaced by the vapor of the distillate would usually become saturated with the vapor and carry some of it out of the apparatus uncondensed.

MAY, 1936

INDUSTRIAL ,4ND ENGINEERING CHEMISTRY Water

I)\ ii”

i egcnd Jaiuratcd Pofnfs 0 = Unsafurated Ponfs

X =

//if/

and Ma/lJoff

-,‘, /

--n

___---

%

/ C C

577

a t less than saturation concentration, it rapidly became anhydrous upon distillation. Hence by the time a distillate sample of required size was taken, the residue would be water-free. The lines for 40, 50, and 60 per cent were omitted because they crowded so closely upon the saturation line as to be indistinguishable on the small-scale diagram. For the determination of the intersection of the various lines of constant water composition and the saturation line, a ternary plot was made of compositions known to be saturated shownand in Figure several8.known The two to bedotted unsaturated. lines show These the limits data are be-

tween which the true saturation line (at the boiling point) must lie. For pure butanol and water the datum of Hill and Malisoff (5) was used, and for the pure butyl acetate and water the datum was determined. It is difficult to obtain saturation data for a system of this In the experimental work to determine the water re~ kind. TURES OF BUTANOL AND BUTYL ACETATEAT THE BOILINGPOINT quired to saturate pure acetate a t the boiling point, a small, round-bottom flask was connected to a condenser with a small pipet fastened to 3 This loss, however, was quite small and it near the point of entrance to the flask. therefore negligible in the ensuing calcuThe flask was heated on a small hot plate lations of vapor and residue composiso that the boiling, while not violent, tions. Table I V shows a sample of was a t least sufficient to agitate the the data and calculations for a typical ,3$ contents of the flask. Supplementary to run. A summary of experimental rethis the flask was rotated by hand as the sults is presented in Table V. 3 water was added. Three separate 25Mor percent 0-6utond in L w d - & Ba~,s gram samples of the acetate were taken, Correlation of Data and the amount of water required to FIGURE 9. CURVEFOR SOLUBILITY OF saturate each one was determined by WATERIN MIXTURESOF BUTANOL AND Consideration of the phase rule (4) BUTYL ACETATE AT THE BOILIiiG POINT means of the criterion already discussed. F = C - P + P where F = No. of degrees of freedom C = No. of individual independent components P = No. of separate phases coexisting at equilibrium ,a’

/a ; 2 tl: $ 2 $ ; ; A h h d Mol Percents OF wATER IN M ~ F~~~~~$3. T~~~~~~pLoTFOR s~~~~~~~~~ 0

‘

$

shows a t once that in a system of three components, when there is only one liquid phase and a gas or vapor phase, there will be three degrees of freedom-namely, temperature, pressure, and the ratio of one of the components to the other two. If pressure is fixed a t atmospheric, it is necessary to fix either the temperature and a composition or two compositions before the system is defined. It is convenient not to bring temperature into the correlation; hence it is necessary to use the concentration of two of the components to fix the system. To portray the equilibrium compositions in a system where two concentrations in one phase must be fixed requires the use of a series of space models, or their equivalent. An entirely satisfactory method for the representation of such data on phase surfaces has not been found, though it is possible to define the system. For one method of correlation in the present investigation, the anhydrous vapor-liquid equilibrium curve for the system n-butanol-n-butyl acetate was drawn, together with the points determined for saturated systems recomputed to the dry basis (Figure 7 ) . The diagram shows that all possible compositions from zero per cent water to saturation must lie between the band defined by the anhydrous and saturated curves. The data for 5, 10, etc., mole per cent water were next plotted on the diagram, and the lines of constant water content in the liquid were thus drawn in. The data points are not shown, but the experimental results are summarized in Table V. The lines of constant water content in Figure 7 represent interpolations from the data of Table V. The data spattered somewhat and in some cases did not extend from the mid-portion of the diagram very far in either direction; hence the uncertain portions were indicated by dotted lines. This uncertain area was not due to lack of attempts to obtain data in that region. The water proved to be such a volatile constituent that, if the residue contained water

Dry Baa5

FIGURE 10. VAPOR-LIQUID EQUILIBRIA FOR SYSTEM BUTANOL-BUTYL ACETATE-WATER

The average percentage of water for the three runs was taken as the desired datum point for the saturation of pure acetate for Figure 8. Points were taken from the smooth solid curve of Figure 8, and the butanol-butyl acetate content was computed to mole per cent on the dry basis. The mole per cent of butanol in the liquid on the dry basis was then plotted against the mole per cent of water in the liquid as shown in Figure 9. From this curve the terminal points for the various percentages of water a t the saturation line of Figure 7 were picked off and marked on the diagram. This method of computing the ternary composition to the dry basis-in other words, plotting as the ratio of the two important components-seems to be advantageous. The vapor-liquid equilibrium can thus be completely defined by two linear-coordinate plots. Equilibrium concentrations in two phases cannot be conveniently represented on ternary diagrams, and space models are not suitable for quantitative work. Obviously Figure 7 does not completely define the liquidvapor equilibrium for the entire system, for it does not give any information as to the water concentration in the vapor. Water concentrations in the vapor are plotted as ordinates in Figure 10. The abscissa is the same as for Figure 7 . Along the right-hand margin of Figure 10 the Stockhardt

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VOL. 28, NO. 5

MAY, 1936

INDUSTRIAL AND ENGINEERING CHEMISTRY

and Hull data for water in tlie liquid are indicated opposite their equilibrium water content in the vapor. The saturation line obtained from the experimental points was located and plotted. Figure 10 shows that, from 60 to 95 mole per cent water in butanol, the vapor in equilibrium is the samenamely, 75 per cent. This is the region of two liquid phases. U'ith more than 95 mole per cent water the system would have one liquid phase. The equilibrium data for this phase were not determined. The above percentages refer to the total water content of the entire system-i. e., in both phases, if two phases are present. On the left-liand 8ide of Figure 10, since there were no data available on the acetate-water system, the saturation point was computed by distilling several mixtures of water and acetate. From t.he observed boiling point of the mixtures (95.5' C .a t 760 mm. pressure) and the vapor pressure of water a.t that temperature ($), the composition of the vapor could be calculated from the usual steam distillation equation. This eompiitatiori gave the following results: n-Butyl acetate

watei

Weiaht Per cent 72.90 27.10

MOIC

Pex Cent

line does not cross the 45' diagonal.

Butyl sleohol

But I ~Ieo~oI

Butyl metate

29.44 70.56

The acetate content of the samples was checked by a saponification analysis and found to agree closely with the computed value. Hence at zero per cent alcohol the water in the vapor was 70.5 per cent. This point marked the other end of the saturation line. The position of the ends of the various iso-water lines were marked off on the sat,uration line from Figure 9 opposite their proper butanol contents, the remaining data points for the unsaturated systems were plotted, and the curves were drawn through these points from the Stockhardt and Hiill data line to the saturation l i e . This method of correlation pictures the system to the best advantage for the distillation mixtures of any compositions. The bunching of points near the saturation line made it desirable to determine more points of low water content. Several a,ttempts were made to obtain data for very low water contents; but even starting with 800-gram batches and distilling out only a 10- or 12-gram samplc, the water would nearly a11 be found in tlie distillate and thus destroy the accuracy of the determination. Space models are not satisfactory for quantitative work, but they do help to visualize the system. Three such inodek were made up in clay on triangular bases of about 9 inches (22.9 cm.) on a side with the saturation line .at the boiling point drawn upon each. The vertical component for each model was the percentage of butanol in the vapor, the percentage of butyl acetate in the vapor, and the percentage of water in the vapor, respectively. P h o t o g r a p h s of these three models are given in Figure 11. The portion of the field for water contents greater than saturation is not shown. A twAimeosiona1 drawing for the space model for butanol in the vapor as the vertical component is shown a t the left in Figure 12. A twodimensional diagram of the model for butyl acetate in the vapor is shown at the right in Figure 12.

Ternary Constant-Boiling Mixture Figure 7 shows that the saturation

579

F~OURE 11. TnIANuDLAR SPACEMODEMOF DISEQU~LIBRIA OF SYSTEM BUTANOL-BUTYL

TILL.ITION

ACB:TATE-wA(PER

The vertiosl distanoee show rnole~eroentagesio thevapor es foil ow.^: fop, butanol: aentei. butyl aeetstei bottom, water.

This observation would lead to the conolusion that thereisno true ternary azeotrope for the system saturated with water. However, this does not preclude the existence of a ternary azeotropefor systems containingless water than that required for saturation. However, the experimentally determined curves (Fignre 10) show that for water contents above 5 mole per cent the water concentration in the vapor is always greater than in tlie liquid. One run (61, TableV) showed a smaller concentration in the vapor than in the liquid, but this effect is probably due to the experimental error a t these ON concentrations (0.05 to 0.30 weight per ceiit). The present investigators had no particular interest in these low water concentrations aiid did not attempt to fill out the field completely. It niay safely he concluded, Iiowever, that a t all concentrations the water contcnt of the vapor is higher than that of the liquid. This conclusion would preclude the possibility of any ternary azeotropic mixture.

OF SPACSMODELS FOR SYSTEM BUTANOLBUTYLACBTATPWATER

FIOURE 12. TWO-DIMENSIONAL DRAW IN^

INDUSTRIAL AND ENGINEERING CHEMISTRY

580

Table V shows that all the water-saturated systems had boiling points in the neighborhood of 90.5" C. These data, however, merely indicate that the action is that of a steam distillation; and even though the boiling temperature may be constant during the distillation of a large portion of a sample, there is no indication of the presence of an azeotropic mixture of constant composition. The Commercial Solvents Company in a private communication stated that they had obtained a constant-boiling mixture with the following composition : Weight Per Cent BuOH 29 BuOAo 40 Hz0 31 Boiling point, 91.4' C.

Mole Per Cent 15.94 14.01 70,05

Dry Basis Weight Mole per cent per cent 42.03 53.00 57.97 47.00

...

...

BuOH BuOBc HzO

Weight Per Cent 14.37 77.04 8.58

separation efficiencies of packed and plate columns using the system n-butanol-n-butyl acetate-water as the experimental mixture in a sixteen-plate, bubble-cap column. They obtained a product boiling a t 90.5" C., but unfortunately they did not analyze the water layer of the product. They did analyze a series of upper layers of distillates with the following results: Run No. BuOH BuOAc H20 BuOH BuOAc

Hz0

BuOH BuOAc

The method of determination was not stated; obviously it would be a solution saturated with water. The percentage of water in the vapor of the Commercial Solvents sample ( 70.05 mole per cent) is in keeping with the water in the vapor rising from saturated solutions as shown in Figure 10. However, according to Figure 7 the percentages of alcohol and acetate do not correspond to any azeotropic mixture. In a system containing an azeotrope of minimum boiling point, the composition may be approached by successive distillation of distillates. This is the action of a fractionating column; therefore, a t the top of a long column, if a true azeotrope exists, the product should have approximately the same composition, no matter what the composition of the residue. In order to check the figures given by the Commercial Solvents Company, the residues from all the equilibrium runs of this investigation were mixed in a large carboy, and enough water was added to saturate the mixture. Three liters of the upper layer were siphoned off and placed in the still pot of a 6-foot (1.5-meter) packed column. The column was operated under total reflux for 7 hours before forward distillation was begun. From this batch of more than 3 liters, about 53 grams of distillate were collected and the two layers were analyzed. This sample was then placed in a microfractionating column (3) and again operated under total reflux for 4 hours before the forward distillation was begun. Ten grams of sample were distilled out and analyzed. The boiling point was identical in both cases, and the difference in composition between the distillate and the residue in the microcolumn was only in the second decimal place. The results of the distillation are as follows: Mole Per Cent 14.55 49.73 35.72

Dry Basia Weight Mole per cent per cent 15.72 22.50 84.28 77.50 ... ...

These results do not agree with those of the Commercial Solvents Company. Another set of data pertinent to this subject is found in the work of Warner and Mechlin (11). They worked on the

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Weight Per Cent 28.7 31.8 32.5 66.1 62.2 61.0 5.2 6.0 6.6 Mole Per Cent 31.1 33.0 33.1 45.7 41.3 39.7 23.2 25 7 27.2 Mole Per Cent, Dry Basis 40.5 44.5 45.6 59.5 55.5 54.5

21.8 74.8 3.4 26.1 57.2 16.7 31.3 68.7

This group of distillates shows considerable variation in composition. If there were a true azeotropic, the composition should be approximately the same for all runs. The compositions in this group vary widely from those given above for the distillation a t the top of a microcolumn and also vary widely from the presumed azeotropic composition reported by the Commercial Solvents Corporation. These experiments present good evidence that there is no true azeotropic mixture in the system butanol-butyl acetatewater. This evidence checks the conclusions drawn from a study of Figures 7 and 10. An apparent minimum boiling point in the neighborhood of 90.5' C. can be found and the percenhage of water in the distillate is approximately constant a t 70 mole per cent over a wide range of residue composition, but these phenomena are connected with distillation from two liquid phases and do not indicate an azeotropic system.

Acknowledgment The authors wish to acknowledge the courtesy of the Commercial Solvents Corporation in furnishing the materials to carry out this work.

Literature Cited (1) Brunjes and Furnas, IND.ENG. CHEM.,27, 396 (1935). (2) Chappius, Trans. mem. bur. i n s t . poides measures, XI11 (1907). (3) Cooper and Fasce, IND. ENG.CHEM.,20,420 (1928). (4) Findlay, "Phase Rule," 5th ed., London, Longmans, Green and Co., 1923. ( 5 ) Hill and Malisoff. J. Am. Chem. SOC.. 48.918 (1926). i6j Othmer, IND. ENG. CHEX.,20, 743'(1928). (7) Ibid., Anal. Ed., 1, 46 (1929). (8) Rosanoff, Bacon, and White, J. Am. Chem. SOC.,36, 1803 (1914). (9) Rosanoff, Schulze, and Dunphy, Ibid., 36,2480 (1914). (10) Stockhardt and Hull, IND. ENG.CHEM.,23, 1438 (1931). (11) Warner and Mechlin, unpublished senior project, Yale University, 1934. .

I

R E C ~ I V B December D 26, 1935. Abstract of a dissertation presented i n partial fulfillment of the requirements for the degree of doctor of philoaophy, Yale University.